Sanjay Kumar Mandal

Background: Scrub typhus is a zoonotic infectious disease caused by the Gram-negative coccobacillus Orientia tsutsugamushi. Meningoencephalitis occurs in two-thirds of all the infected cases. Aims and Objectives: The study of these cases was conducted to study the clinical, biochemical, and hematological features of scrub typhus meningoencephalitis. Materials and Methods: We included 12 patients who were admitted in the General Medicine Ward of Medical College and Hospital, Kolkata, between May 2021 and July 2022. The serum scrub typhus immunoglobulin M (IgM) test was used to diagnose the cases after ruling out dengue, malaria, leptospirosis, bacterial, tubercular, and viral meningoencephalitis. Results: A triad of fever, altered sensorium, and meningeal signs were present in all of the cases. 2 patients had seizures, 1 patient had lateral rectus palsy, 1 patient had a generalized maculopapular rash, and eschar was seen in only 2 cases. The most common laboratory abnormalities were hyponatremia, anemia, and transaminitis (each 83.33%). 8 cases (66.7%) had a combination of anemia, hyponatremia, and transaminitis. Cerebrospinal fluid abnormalities included protein elevation (75%) and lymphocytic pleocytosis (83.33%). Scrub typhus IgM was positive in all of them. All the cases showed excellent response to doxycycline. Conclusion: A high degree of clinical suspicion is required to diagnose scrub typhus meningoencephalitis. The eschar is detected in very few cases and it may be difficult to recognize the same among the dark-skinned Indian population. However, as per our study, any case of meningoencephalitis with a combination of anemia, hyponatremia, and deranged liver function tests should always raise the possibility of the aforementioned disease and doxycycline therapy must be started promptly.

The spontaneous electrical polarization/ magnetization in influence of magnetic flux/electric flux of the magneto-electric composite attain extensive research. We have fabricated Ni0.5Co0.5Fe2O4-PbZr0.58Ti0.42O3 magnetoelectric nanocomposite having weight ratio of 30:70 through the low temperature “Pyrophoric reaction process”. The structural and surface characterizations of the composite have been confirmed by X-ray diffraction technique and scanning electron micrographs, respectively. The magnetic field dependent electrical memory effect has been examined by the study of direct current electrical characterization (current versus voltage profile) of the composite at room temperature. The current follows the irreversible path as a function of applied direct current electric field. In applied magnetic field, 21% open circuit current increases at room temperature. The current versus voltage characteristic of the composite expresses non Ohmic behavior and follows the Child’s Law. On the other side, for the alignment of magnetic dipoles of the piezo-magnetic phase of magnetoelectric composite with space charge effect, the current increases with increase of applied magnetic field, where the maximum change is found to ~ 28% in the measured range.

Detailed analysis on structural, dielectric and ac electrical transport with dc magnetic field variation and magnetoelectric response are studied on semiconductor based multiferroic La_0.7Sr_0.3MnO₃ - ZnO nanocomposites. The impedance data is observed to gradually enhance with magnetic field due to the strain developed in the sample, hampering the charge flow in the system. The nanocomposites display prominent magneto-impedance (∼87%) and magnetodielectric (∼35%) at room temperature. Nyquist plots are fitted utilizing two resistance-capacitor parallel circuits at varying magnetic fields demonstrating the governing role of La_0.7Sr_0.3MnO₃ and ZnO grain boundaries. The grain boundary resistance of La_0.7Sr_0.3MnO₃ decreases with field due to the depinning of domain walls from the grain boundary pinning centers and therefore improving the spin dependent transport mechanism while the grain boundary resistance of ZnO increases with field due to the scattering of the charge carrier. The magnetoelectric coupling investigated at a frequency of 1 kHz is accomplished in both longitudinal and transverse mode. Further, the magnetoelectric voltage induced by ac magnetic field executes a linear magnetoelectric response. The viewed magnetoelectric coupling might be in consequence of the field influenced magnetostriction of the piezomagnetic element of the composites. Such multiferroic material with tuning ac electrical property with magnetic field alongside magnetoelectric response can be pertinent in future solid-state microelectronic devices and sensor applications.

Magnetoelectric Zn0.5Co0.5Fe2O4 - PbZr0.58Ti0.42O3 nanocomposites are synthesized considering chemical reaction process at low temperature and solid-state reaction technique. Structural characterization is performed by X-ray diffraction analysis, which shows two types of nanometric grains coexisting simultaneously. The materials surface morphology displays that the fabrication method is quite effective for preparation of nanocomposites. Crystallite size of different constituent phases is observed to in manometer range. The dependency of temperature on electrical response and dielectric constant of nanocomposites are analyzed with a variation of frequency. The dielectric constant with temperature decreases attributing the thermal excitation of electrons. Moreover, we have evaluated the magnetoelectric coefficient in two configurations (longitudinal and transverse) with increasing applied magnetic field. The coupling coefficient is observed to similar to 0.8 mV/cm-Oe in transverse configuration, whereas in longitudinal configuration it is increasing in behavior with measured magnetic field. At room temperature, the observing magnetoelectric coupling may be as a cause of magnetic field dependent strain transfer to the piezoelectric phase to the piezomagnetic phase of the nanocomposites.

Magnetoelectric composites of xLaFeO₃–(1 − x)Pb(Zr_0.58Ti_0.42)O₃ (x = 0.2 and 0.3) have been prepared by pyrophoric reaction process. The observed room temperature magnetoelectric coefficient is enhanced with the increase of LaFeO₃ content in nanocomposites. The maximum value of magnetoelectric coupling is found to be ∼1.5 mV/cm-Oe and ∼0.3 mV/cm-Oe, which may be due to the strain mediation of piezomagnetic phase and magnetodielectric property of the material. The frequency dependent AC conductivity at several temperatures indicates the thermally activated conduction process in the system. The electrical conductivity (both AC and DC) shows positive temperature coefficient resistance effect of the system where AC conductivity obeys Jonscher’s power law. It demonstrates the hopping mechanism via small as well as large polaronic conduction process in the system. Maximum change of magnetoimpedance (∼185%) is observed at a frequency of 100 Hz at room temperature. The observed magnetoimpedance effect can be explained considering the skin effect. The magnetocapacitance effect shows the maximum value (∼60%) at lower frequency regime at room temperature attributing the evidence of Maxwell–Wagner interfacial or space charge polarization in the sample. At room temperature the magnetic field dependent capacitance of these samples is corroborating the evidence of magnetoelectric coupling.

Magnetoelectric composites are promising materials for their physical properties such as spontaneous electrical polarization or magnetization with the application of magnetic or electric field. In addition, Spinel ferrite based magnetoelectric composite materials absorb a range of light energy, which offers a lot of physical phenomena behind the light-dependent magnetoelectric properties of the composite. The piezoelectric organic polymer based magnetoelectric composite of Zn_0.2Co_0.8Fe₂O₄-poly(vinylidene fluoride) flexible film has been fabricated by a chemical pyrophoric reaction process followed by a solution casting process. Structural and surface morphologies of the composite film have been studied. The visible light and applied magnetic field dependent AC electrical properties of the composite flexible film have been investigated at room temperature which reveals that the maximum change in impedance is found to be ∼10% and ∼20%, respectively. However, with an influence of both the light and the magnetic field, the impedance of the composite film is largely changed attributing that the excited electron may get a low resistive path through the grain and grain boundaries where the maximum change in impedance is found to be ∼30%. This result further is confirmed from the change of grain and grain boundary resistance and capacitance through the fitting of Nyquist plots. The present work provides information about the optically and magnetically influenced physical properties of the composite flexible film, which will be expanded for multiferroic magnetoelectric device applications.